Need help with my course on memory mapping and stuff

I have got a begginner's course in computer organisation this semester. The course consists of the basic stuff like types of memories and memory hierarchy with the detailed description of each etc etc.
Now, what i really dont get is memmory mapping and how exactly data is read and written on main memory, cache memory or may be associative memory.
Is there any tutorial available on the internet that can describe all this in detail but which starts from a basic level?
Please dont suggest any reference book, i have lost my library card :(